Differential Effect of Renal Cortical and Medullary Interstitial Fluid Calcium on Blood Pressure Regulation in Salt-Sensitive Hypertension.

BACKGROUND Hypercalciuria is a frequent characteristic of hypertension. In this report we extend our earlier studies investigating the role of renal interstitial fluid calcium (ISF_Ca)²⁺ as a link between urinary calcium excretion and blood pressure in the Dahl salt-sensitive (DS) hypertensive model. METHODS Dahl salt-sensitive and salt-resistant (DR) rats were placed on control (0.45%) and high (8%) salt diets to determine if changes in renal cortical and medullary ISF_Ca ²⁺correlated with changes in urinary calcium excretion and blood pressure. RESULTS We observed that renal ISF_Ca ²⁺ was predicted by urinary calcium excretion (P < 0.05) in DS rats but not DR rats. Renal cortical ISF_Ca ²⁺ was negatively associated with blood pressure (P < 0.03) while renal medullary ISF_Ca ²⁺ was positively associated with blood pressure in DS rats (P < 0.04). In contrast, neither urinary calcium excretion nor renal ISF_Ca ²⁺ was associated with blood pressure in the DR rats under the conditions of this study. CONCLUSION We interpret these findings to suggest that decreased renal cortical ISF_Ca ²⁺ plays a role in the increase in blood pressure following a high salt diet in salt hypertension perhaps by mediating renal vasoconstriction; the role of medullary calcium remains to be fully understood. Further studies are needed to determine the mechanism of the altered renal ISF_Ca ²⁺ and its role in blood pressure regulation. [ABSTRACT FROM AUTHOR]